/*
 *  Copyright (c) 2017 Uber Technologies, Inc. (hoodie-dev-group@uber.com)
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *           http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 *
 */

package com.uber.hoodie.hadoop;

import com.uber.hoodie.exception.HoodieException;
import java.io.IOException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.mapred.RecordReader;

/**
 * Provides Iterator Interface to iterate value entries read from record reader
 *
 * @param <K> Key Type
 * @param <V> Value Type
 */
public class RecordReaderValueIterator<K, V> implements Iterator<V> {

  public static final Log LOG = LogFactory.getLog(RecordReaderValueIterator.class);

  private final RecordReader<K, V> reader;
  private V nextVal = null;

  /**
   * Construct RecordReaderValueIterator
   *
   * @param reader reader
   */
  public RecordReaderValueIterator(RecordReader<K, V> reader) {
    this.reader = reader;
  }

  @Override
  public boolean hasNext() {
    if (nextVal == null) {
      K key = reader.createKey();
      V val = reader.createValue();
      try {
        boolean notDone = reader.next(key, val);
        if (!notDone) {
          return false;
        }
        this.nextVal = val;
      } catch (IOException e) {
        LOG.error("Got error reading next record from record reader");
        throw new HoodieException(e);
      }
    }
    return true;
  }

  @Override
  public V next() {
    if (!hasNext()) {
      throw new NoSuchElementException("Make sure you are following iterator contract.");
    }
    V retVal = this.nextVal;
    this.nextVal = null;
    return retVal;
  }

  public void close() throws IOException {
    this.reader.close();
  }
}
